Now z is equivalent to (variable - mean) / standard deviation. Or z= (131.5 - 100) / 15 = 2.1. From the normal distribution table the cumulative probability till z= 2.1 is 0.4821. As we need the probability of a person with an IQ greater than 131.5 it is equal to 0.5 - 0.4821 = 0.0179.